Exclusive is the problem word. I wish they would change it to, say, "at least 85% [or 90%] business use". After all, those who have a business office at some other location probably play computer games from time to time, on their office computer, or watch the game on the "business" TV in their lobby, etc. Just because someone has his washer and dryer down there, or park their exercise equipment, or even where their kids do their homework and use the printer, or where they spend their weekends watching streaming video or playing internet games does not make it not a "real" office, if that is where they regularly work to generate their taxable income. When my kids were in school they often used my office to print their school projects, etc. But merely because it was a separate office I rented and operated out of, I did not have to measure that use. I bought 'personal use' paper as needed, but otherwise nothing.